This invention relates to foundry equipment and more particularly to a multi-tube continuous sand muller for mixing sand and binder materials to produce molds and/or cores.
Recently developed quick setting resin binder systems for sand molds or cores require only short working times and strip times. Such systems do not require baking for proper set. Although the quick setting feature is an important advantage production wise, it can create a serious problem in the maintenance of continuous muller equipment. Once the resin binder has been added to the sand, some of the resins tend to air-set without the addition of catalyst. When air-setting occurs, the sand/resin binder mixture may lump in the mixing tubes, creating variations in blending of materials, and even clogging of the equipment.
Commonly owned U.S. Pat. No. 4,039,169, entitled CONTINUOUS SAND MULLER and issued on Aug. 2, 1977, to Bartholomew discloses a continuous, three-tube sand muller which provides a pair of oppositely rotating premixing tubes and a main mixing tube. Sand and a binder additive are preblended in each of the premixing tubes, and the premixes from the two premixing tubes are combined and blended in a single, larger primary mixing tube. The completely blended materials are then deposited by the primary tube into a core box or mold. The mixing tubes are driven by a pulley and belt drive. The drive rotates the augers in the premixing tubes at the same rate, but counter-rotational to each other. The drive also rotates the primary mixing auger in the main or primary mixing tube at a controlled rate capable of receiving the full output of the two premixing augers.
Although a three-tube muller, as described in the aforementioned patent, is well adapted to handle most binder resin systems, the newer resin binders that tend to air-set without the presence of catalyst tend to create clogging problems in the premixing tubes. This can cause a buildup of materials in the premixing tubes as well as in the primary tube. Cleaning of the premixing tubes becomes more frequent, and accelerated wear problems may be experienced. In addition, some variation in the loads on any of the three mixing augers due to lumps in the materials, partial resin binder curing, or for any reason, can cause belt slippage, and further aggravate non-uniform mixing of materials.
U.S. Pat. No. 3,268,214, entitled COMBINED MIXER AND CONVEYOR UNITS and issued on Aug. 23, 1966, to Higgs also discloses a multi-tube muller or combined mixer and conveyor units. In one embodiment, a two-tube muller is disclosed. In another embodiment, a three-tube muller is disclosed. Multiple motors are used to drive the mixers.
Even though the three-tube mixer has proven to be an important advance over the prior single tube continuous mullers, and has solved many of the problems associated with the use of quick setting resin binder systems, there has been a need for further improvement in such equipment, particularly to solve the problems created by resin binders which tend to air cure.